Resinoid bonded abrasive wheels



United 2,952,529 RESINOID BONDED ABRASIVE ELS H. Nathan Stone, Worcester, Mass, State Abrasive Products Company, a corporation of Massachusetts assignor to Bay Westboro, Mass,

This invention relates to resinoid bonded abrasive wheels and is particularly concerned with abrasive wheels of the type described which are adapted for grinding of stainless steel billets and at the same time contain no sulfur or metallic sulfides.

For many years it has been the practice to use in the bonds of grinding wheels intended for snagging stainless steel billets sulfur, usually in the form of a metallic sulfide, as a grinding aid. The results obtained with such grinding wheels have been very satisfactory. However, from time to time, the recurring shortage of nickel makes it necessary to recover the nickel present in the swarf resulting from the grinding of stainless steel. The sulfur present in the swarf as a result of using grinding wheels containing sulfides makes the recovery of nickel both diflicult and expensive. Consequently, there has been a need for a sulfur-free billet grinding wheel which has a relatively high cutting rate on the tough stainless steel ingots and that performs with approximately the same eificiency as wheels containing sulfur.

It is therefore an object of the present invention to provide grinding Wheels for stainless steel billets which contain no sulfur or sulfides.

Another object of the invention is to provide grinding wheels of the character described which, in grinding stain- .less steels, have relatively high cutting rates and efiiciencies approximately equal to the wheels previously used.

A further object of the present invention is to provide grinding wheels of the character described which may be manufactured easily and inexpensively.

Other objects and advantages of the present invention will be apparent from the following description.

It has been discovered that satisfactory results can be obtained in snagging operations on stainless steel billets with grinding wheels which contain no sulfur or metallic sulfide but instead have in their bonds as filler a mixture of cryolite and ammonium chloride in suitable proportions. In a number of tests, wheels made according to the present invention were compared with standard zinc sulfide containing grinding wheels of the type comlmercially used for grinding stainless steel. It was found that the metal removal rates of the sulfide containing wheels are approximately equalled or even exceeded by the grinding Wheels containing no sulfide and the novel combination of fillers described herein.

Although other methods may be employed, the following is a typical procedure for manufacturing an abrasive Wheel using a sulfur-free bond of the character with sulfide-containing tent Patented Sept. 13, 1960 Example I Wt. in lbs. Fused alumina abrasive (14 grit) 71.0 Powdered phenol-formaldehyde resin bond (such as Bakelite BR-2417) 10.76 Powdered cryolite (approximately 200 mesh) 14.91 Granular ammonium chloride (30 mesh and finer) 2.35

Powdered lime (CaO) Furfural, -300 cc.

Enough furfural within the abovementioned limits is added to the abrasive to properly wet the latter and the abrasive and furfural are thoroughly mixed. The dry ingredients which have been blended together are then added to the furfural-moistened abrasive grain and mixed until a substantially dry, free flowing, granular mass is obtained. A mold of the proper size is then filled with the abrasive-bond mix and placed in a hot press. The temperature is maintained between 300 F.- 320 F. for 1 hour. Then the pressed wheel is taken from the mold and its cure is completed by holding it at a temperature of 350 for 10 hours. After cooling, the wheel, which comprises by volume 54% abrasive and 46% bond, is finished in the conventional manner Well known to those skilled in the art.

It will be understood that the invention is not limited to hot pressed abrasive wheels but is also susceptible of use with cold pressed wheels. Also, of course, other types of heat-hardenable resinoid bonds, such as anilineforrnaldehyde and resorcinol-formaldehyde resins and the like, may be employed instead of the phenol-formaldehyde resin described above. As described more specifically below, there may also be considerable variation in the proportions of the ingredients used.

In Example I the cryolite constitutes about 33% by volume of the bond and the ammonium chloride amounts to about 10% by volume thereof. It has been found that good results are obtained when the bond comprises from about 40% to 45% by volume of the mixture of fillers. As shown by the following examples the ratio of cryolite to ammonium chloride may vary considerably although the cryolite is always employed in larger amounts.

In the examples set forth below the comparative grinding tests were carried out on No. 410 stainless steel using 20" x 2 /2 x 6 abrasive wheels running at 8500 s.f.p.m. In each example the wheel identified as C contained cryolite and ammonium chloride, but was sulfur-free and the wheel identified as S was typical of wheels commercially used in snagging stainless steel (approximately 200 mesh) 0.95

billets and included zinc sulfide as a filler in the bond.

Both wheels, however, had approximately the same volume ratios of abrasive grain to bond.

Example 11 3 included 17% by volume of zinc sulfide as a grinding aid. The results (averages) were as follows:

M W Wheel Metal Re- Wheel Efliciency,

moved, Loss, M/W lbs/hr. infi/hr.

It will be seen that the metal removal rate of wheel C is somewhat better than that of wheel S while the efiiciencies are also in the same order and differ only slightly.

' Example 111 An abrasive wheel with fused alumina abrasive containing 27 volume percent of cryolite and 14 volume percent of ammonium chloride in the resinoid bond was tested in comparison with an abrasive wheel including in the bond 16% by volume of zinc sulfide. The results (averages) were:

M W Wheel Metal Re- Wheel Eflieiency,

moved, Loss, MI W lbs/hr. ind/hr.

While the efliciency of wheel S was slightly better than that of wheel C, the latter had a metal removal rate about 18% higher than that of wheel S.

Example IV A fused alumina abrasive wheel the resinoid bond of which contained, by volume, 30% cryolite and 12% ammonium chloride, was tested in comparison with an abrasive wheel of similar structure that included 16% by volume of zinc sulfide as a filler in the bond. The results (averages) were:

M W Wheel Metal Re- Wheel Efficiency,

moved, Loss, M/W lbs./hr. infi/hr.

The cutting rate of wheel C was materially higher than that of wheel S although the difference in ethciencies was so small as to be insignificant.

Example V M W Wheel Metal Re- Wheel Efficiency,

moved, Loss, M/W lbs/hr. infi/hr.

O 29. 6 33. 7 O. 88 s 23.0 26.5 0. s7 7 The foregoing series of tests makes it evident that novel, sulfur-free abrasive wheels made in accordance with the present invention perform substantially as well or better than comparable, standard abrasive wheels that contain metallic sulfide fillers. Not only, therefore, are satisfactory grinding results obtained, but also recovery of nickel from the swarf resulting from the grinding of stainless steels is made easier and less expensive.

As pointed out above, the total volume percentages of cryolite and annnonium chloride in the bonds of abrasive wheels according to the present invention can be between about 40% and 45%. The cryolite may vary from about 20% to 40% by volume of the bond and the ammonium chloride may comprise by volume from about 5% to 15% of the bond. Although the cryolite should be finely divided and particles of a size which will pass through a 200 mesh screen are preferred, it is possible to employ cryolite in particle sizes ranging from about mesh to about 325 mesh. The ammonium chloride should be at least fine enough to pass through a 30* mesh screen but should not be extremely fine since it is somewhat hydroscopic and in a very small state of subdivision this may cause difliculties. In general, the ammonium chloride should not be finer than approximately 100 mesh. It will also, of course, be understood that the abrasive grain may vary in particle size and amount and that abrasive mixtures of difierent grit sizes may be employed. The lime employed in the typical wheel described is convent-ionally used as an absorbent for water resulting from the cure of the resin of the bond, thus the chance of the wheel bloating during curing. The amount used is not too critical but enough should be used to accomplish the desired purpose. The necessary amounts for different types of resin are known to those skilled in the art.

As indicated above, the present invention is subject to variation and modification of the specific details set forth in the preceding description without departure from the spirit thereof. Accordingly, it is not intended that the invention shall be considered as limited by the details of disclosure except as required by the appended claims.

I claim:

'1. An abrasive sulfur tree wheel which consists of abrasive granules and a bond, said bond being free of sulfur and comprising essentially a heat-hardenable resin, about 27% by volume of cryolite and about 14% by volume of ammonium chloride.

2. An abrasive sulfur free wheel which consists of abrasive granules and a bond, said bond being free of sulfur and comprising essentially a heat-hardenable resin and as a filler mixture about 20% to 40% by volume of cryolite and about 5% to 15% by volume of ammonium chloride, the total volume of said filler mixture being from about 40% to 45%.

3. An abrasive sulfur free wheel as set forth in claim 1 in which the mesh sizes of the fillers fall Within the following approximate limits-cryolite: 100 mesh-325 mesh, ammonium chloride: 30 mesh-J 00 mesh.

4. An abrasive sulfur free wheel as set forth in claim 2 in which the mesh sizes of the fillers fall within the following approximate limits-cryolite: 100 mesh-32S mesh, ammonium chloride: 30 mesh-100 mesh.

References Cited in the file of this patent UNITED STATES PATENTS 2,333,429 Kuzmick Nov. 2, 1943 2,534,806 Webber et a1. Dec. 19, 1950 2,811,430 Gregor et al. Oct. 29, 1957 2,860,960 Gregor Nov. 18, 1958 2,860,961 Gregor et al Nov. 18, 1958 

2. AN ABRASIVE SULFUR FREE WHEEL WHICH CONSISTS OF ABRASIVE GRANULES AND A BOND, SAID BOND BEING FREE OF SULFUR AND COMPRISING ESSENTIALLY A HEAT-HARDENABLE RESIN AND AS A FILLER MIXTURE ABOUT 20% TO 40% BY VOLUME OF CRYOLITE AND ABOUT 5% TO 15% BY VOLUME OF AMMONIUM CHLORIDE, THE TOTAL VOLUME OF SAID FILLER MIXTURE BEING FROM ABOUT 40% TO 45%. 